Electron gun having concave coined grid and annular rib

ABSTRACT

A plural electrode electron gun comprises a cathode and related first and second grid electrodes having compatibly shaped adjacent functional surfaces. The apertured functional portion of the first grid is formed in a concave manner with the concavity thereof facing away from the cathode; the first grid having an aperture concavely coined within the concavity. The superfluous material resultant from the aperture coining is utilized adjacent thereto in forming an axially oriented annular rib which is shaped to protrude within the concavity. The second grid electrode has a compatibly shaped functional portion formed to functionally cooperate with the concave portion of the first grid electrode.

United States Patent Primary Examiner- Robert Segal Attorneys-Norman .1.OMalley, Donald R. Castle and Frederick H. Rinn ABSTRACT: A pluralelectrode electron gun comprises a cathode and related first and secondgrid electrodes having compatibly shaped adjacent functional surfaces.The apertured functional portion of the first grid is formed in aconcave manner with the concavity thereof facing away from the cathode;the first grid having an aperture concavely coined within the concavity.The superfluous material resultant from the aperture coining is utilizedadjacent thereto in forming an axially oriented annular rib which isshaped to protrude within the concavity. The second grid electrode has acompatibly shaped functional portion formed to functionally cooperatewith the concave portion of the first grid electrode.

ELECTRON GUN HAVING CONCAVE COINED G AND ANNULAR RIB BACKGROUND OF THEINVENTION This invention relates to cathode ray tubes and moreparticularly to the relationship between the first and second gridelectrodes in an electron gun structure.

In certain types of CRT electron guns most of the cathode structure isusually encompassed by a cup-shaped first grid electrode wherein theapertured closed end is usually planar. In those instances where a thinfirst grid aperture is desired, a coined aperture shaping may beemployed wherein the superfluous material resultant from coining isusually accommodated in an annular takeup-rib formed adjacent thecoining which promotes flattening of the aperture. This rib is alsointended to function as a strengthening structure in an endeavor tominimize in-and-out expansive and contractive thermal movement of thesubstantially planar closed end of the grid, but positional stability isdifficult to maintain when a planar surface is adjacent the heatedcathode. Any in-and-out movement of the functional planar grid surfaceis deleterious as it directly affects consistent spacing between thefirst and second grid apertures. Since the critical spacing between theapertured surfaces of the first and second grid electrodes is usually ofa relatively close dimension, it has been conventicnal practice to formthe first grid rib inwardly away from the outer surface thereof.

In first grids employing a regular uncoined aperture, one or moreinspection openings have been sometimes incorporated into the sidewallor skirt portion of the first grid electrode to facilitate visualinspection and adjustment of the spacing between the cathode and thefirst grid aperture. When coined apertures are employed, the inherentinwardly extending takeup-rib obstructs the view of the cathode-gridaperture spacing and thereby eliminates the desired utility of theinspection opening.

OBJECTS AND SUMMARY OF THE INVENTION at It is an object of the inventionto reduce the aforementioned disadvantages and to provide an improvedcathode ray tube electron gun structure wherein the functional surfacesof the first and second grid electrodes have a discretely formedrelationship.

A further object is to provide an electron gun structure wherein thecathode to first grid electrode spacing can be expeditiously effectedand substantially stabilized.

Another object is the provision of a first grid electrode structurewherein the apertured end closure and skirt portions are formed in amanner to achieve and maintain accurate spacing of the cathodepositioned therein.

The foregoing objects are achieved in one aspect of the invention by theprovision of an electron gun comprising a cathode and a plurality ofsequential electrodes including first and second grid electrodes havingadjacent related functional surfaces. The functional portion of thefirst grid is formed in a concave manner to provide a concavity ofdefined depth. A beam defining aperture therein has the immediatelysurrounding material reduced in thickness by concave coining orientedwithin the concavity. The superfluous material resultant from thecoining is utilized in forming an axially oriented annular rib whichprotrudes within the concavity adjacent the coined aperture. Thus, thereis no rib material extending beyond the flattened surface of theaperture toward the cathode. The second grid electrode has an aperturedfunctional portion that is formed to be compatible with the concavefunctional portion of the first grid.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 11 is a sectional view of acathode ray tube wherein the invention is utilized;

FIG. 2 is an enlarged sectional View of a portion of the electron gunstructure employing the invention;

FIG. 3 is a plan view illustrating the end closure portion of the firstgrid electrode taken along the line 3--3 of FIG. 2; and

lFllG. 4 is a sectional view of another embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT For a better understanding ofthe present invention, together with other and further objects,advantages, and capa bilities thereof, reference is made to thefollowing specifics tion and appended claims in connection with theaforedescribed drawings.

With reference to the drawings, there is shown in FIG. 1, a cathode raytube It having an axis 112 and comprising an en velope 13 whereof theface plate or viewing panel 11% has a cathodoluminescent screen 17formed on the inner surface thereof. Positioned within the neck portion19 of the envelope is at least one electron gun structure 21, notdetailed, which includes a cathode and a plurality of sequentiallyarranged electrodes. These cooperating electrode elements are formed andspaced to provide the source, acceleration and control of the electronbeam 23 which is controllably deflected by coils 25, positionedexternally of the envelope, to effect predetermined irnpingement on thescreen 117 and thereby provide an image display raster therein. Asshown, the axes of the electron gun 21 and the tube 11 are substantiallycoincidental, but such axes relationship is not intended to be limiting.

In referring to FIG. 2, there is shown an enlarged sectional view of therear portion of the electron gun structure M which is oriented in theneck portion 119, not shown. This portion of the electron gunZlcomprises a thermionic cathode structure 27 having an external electronemissive area 29 and an internally positioned heating element 31. By wayof illustration, a substantially cup-shaped first grid electrode 33 isshown but is not to be considered limiting. This first grid ispositioned to encompass at least part of the cathode .27. A second gridelectrode 35 is oriented in spaced axial relationship to the first grid33, and a first anode electrode 37, a portion of which is shown, isspacedly positioned therebeyond. Conventional means, such as studs andglass rods, are utilized to support these several electrodes in axialalignment, but since such support means are not part of the inventionthey are not illustrated in the drawings. To add clarity to thedescription, certain illustrative dimensions will be given in the courseof this specification, but in no manner are they to be consideredlimiting.

In greater detail, with reference to FIGS. 2 and 3, the first gridelectrode 33, which for example may be formed from nonmagnetic stainlesssteel of substantially 0.007 inches thickness, has a substantiallycylindrical skirt portion 39 and a functional or end closure portion 41which is integrally joined to the skirt portion 29 at a commonperipheral transition rim 43. The functional or closure portion 41,which has a material thickness t", is fonned as an inwardly orientedconcave shaping providing a concavity 44 of defined depth e" to impartstrengthened positional stability to the closure having inner and outersurfaces 45 and 47 respectively. A beam-shaping aperture 49 is formed asa substantially axially oriented bore in the concave closure portion 41,and the closure material thickness immediately surrounding the aperturei9 is reduced by a concave coining 48 within the concavity relative tothe outer surface i7 of the closure portion $11. By this coiningoperation a beneficial reduction in thickness of material t' is achievedat the aperture d9. This reduced aperture thickness in conjunction withthe distance 0", such as 0.005 inches, between the emissive portion 29of the cathode 2'7 and the inner surface d5 of the first grid functionalor closure portion 41 constitutes a critical dimension (oi-t) which isdesirably small, being in the order of 0.008 inches. The concave coining48 or gradual reduction in material thickness is effected within asubstantially axially oriented circular area diametrically dimensionedby a a" which may be approximately 0.090 inches. The superfluousmaterial displaced as a result of the coining operation is utilized inthe forming of an axially oriented annular support rib 511 whichprotrudes within the concavity 44 as part of the outer surface 47 of theclosure adjacent the coined area 48. This annular rib 57 is laterallydefined by a diametrical dimension "b" having a value such as 0.150inches. It has an overall height "d" of approximately 0.015 inches whichis less that the overall concavity depth e" of the closure 41, thatbeing approximately 0.020 inch. At no time should the support rib 51extend above the plane ofthe peripheral rim 43.

At least two substantially diametrically opposed inspection windows 55are formed in substantially the skirt portion 39 at substantially theperipheral transition rim 43. By being edged into the periphery of theclosure portion 41 these window areas 55 afiord ample unobstructedviewing of the cathode area 29 in relation to the inner surface of thebeam forming aperture region 49. By this means the cathode can beaccurately positioned and inspected.

A second grid electrode 35 having a material thickness such as 0.007inchesis spacedly positioned relative to the concave outer. surface ofthe first grid electrode 33, as denoted by the spacing f ofapproximately 0.025 inches. The second grid functional or end closureportion 57 has inner and outer surfaces 59 and 61 respectively with asubstantially uniform material thickness therebetween. An axiallyrelated central portion 63 having an axial aperture 65 therein is formedto protrude outwardly from a substantially flat circumferential portion67, by a dimension n", toward the concavity of the first grid electrode33. This protruding dimension n may be for example 0.020 inch, which inconjunction with the spacing of f provides the desired interelectrodeaperture spacing .r". In keeping with the invention, the dimension "n"may be larger or smaller than the spacing 1" depending on theinterelectr'ode spacing .r desired. In this instance, the centralprotruding portion 63 has diametrical dimension v" which is less thanthe diametrical dimension b" of the first grid annular support rib 51,but there may be grid relationships wherein "v" is greater than b".

The electron gun structure 21 further comprises a substantiallycylindrical first anode electrode 37 located screenward of and in spacedaxial relationship to the second grid electrode 35. Additionalsequentially positioned cooperating electrodes may be included in thegun structure in accordance with the particular gun design utilized.

With reference to FIG. 4, there is shown another embodiment of a firstgrid electrode structure 33' wherein the skirt portion is eliminated.Such grid construction is sometimes utilized in certain types of gunassemblies. By this invention, the function portion 41 is concavelyformed to provide a concavity 44' is having a defined depth e". Thecoined aperture 48' and the supporting rib 51 are structures similar tocounterparts already described. The annular rib 51' protrudes within theconcavity 44', but does not extend above the plane of the peripheral rim43'. A first grid of this structure is suitably positioned by supportmeans, not shown, which are extended in a conventional manner beyond theperipheral rim 43' to be embedded, for example, in commonly employedglass support means, not detailed.

Thus, an improved cathode ray tube electron gun structure is providedwherein the functional closure surface 41 of the fast grid electrode 33is discretely formed to effect a stabilized cooperative relationshipwith the compatibly formed second grid electrode 35. Additionally, thefirst grid electrode 33 is formed in a manner to facilitate opticaladjustment of the cathode thereby expeditiously effectingcathode-to-first-grid electrode spacing of desired accuracy. While theaforedescribed structural recitations are applicable to cathode ray tubeelectron guns of any size, they are particularly advantageous inconstructing miniaturized gun assemblies having critically closeelectrode spacings and utilizing electrode apertures of small sizes, forexample, those of 0.020 inch and smaller.

While there has been shown and described what are at present consideredthe preferred embodiments of the invention, it will be obvious to thoseskilled in the art that various changes and modifications may be madetherein without departing from the scope of the invention as defined bythe appended claims.

I claim:

1. A cathode ray tube electron gun having a cathode and a plurality ofsequential electrodes formed and spaced therein to provide the source,acceleration and control of an electron beam, said gun having an axisand comprising in combination: a first grid electrode spacedlypositioned relative to said cathode, said first grid having a functionalportion with an axis therethrough, said portion being formed in aconcave manner having a defined depth with the concavity thereof facingaway from said cathode, a beam control aperture formed as asubstantially axial bore through said functional portion, said materialthickness immediately surrounding said aperture being of reducedthickness provided by concave coining of the material relative to theouter surface of said concavity; an axially oriented annular rib formedin said functional portion in a manner to protrude within said concavelyadjacent said coined aperture therein, said protruding rim being of aheight not exceeding the depth of the concavity of said functionalportion; and a second grid electrode having an axis and a functionalportion protruding outwardly toward the concavity of said first gridelectrode, said functional portion having a diameter less than that ofsaid annular rib.

2. A cathode ray tube electron gun according to claim 1 wherein saidfirst grid electrode is formed as a substantially cup-shaped structurehaving a substantially cylindrical skirt portion joined to said concavefunctional portion at a common peripheral transition rim; said concavityformed functional portion providing an end closure for said cup-shapedstructure.

3. A cathode ray tube electron gun according to claim 2 wherein saidsubstantially cup-shaped first grid electrode has at least twosubstantially opposed inspection openings formed in said skirt andfunctional portions at substantially the peripheral transition rimthereof.

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1. A cathode ray tube electron gun having a cathode and a plurality ofsequential electrodes formed and spaced therein to provide the source,acceleration and control of an electron beam, said gun having an axisand comprising in combination: a first grid electrode spacedlypositioned relative to said cathode, said first grid having a functionalportion with an axis therethrough, said portion being formed in aconcave manner having a defined depth with the concavity thereof facingaway from said cathode, a beam control aperture formed as asubstantially axial bore through said functional portion, said materialthickness immediately surrounding said aperture being of reducedthickness provided by concave coining of the material relative to theouter surface of said concavity; an axially oriented annular rib formedin said functional portion in a manner to protrude within said concavityadjacent said coined aperture therein, said protruding rim being of aheight not exceeding the depth of the concavity of said functionalportion; and a second grid electrode having an axis and a functionalportion protruding outwardly toward the concavity of said first gridelectrode, said functional portion having a diameter less than that ofsaid annular rib.
 2. A cathode ray tube electron gun according to claim1 wherein said first grid electrode is formed as a substantiallycup-shaped structure having a substantially cylindrical skirt portionjoined to said concave functional portion at a common peripheraltransition rim; said concavity formed functional portion providing anend closure for said cup-shaped structure.
 3. A cathode ray tubeelectron gun according to claim 2 wherein said substantially cup-shapedfirst grid electrode has at least two substantially opposed inspectionopenings formed in said skirt and functional portions at substantiallythe peripheral transition rim thereof.